Method, computer program, electronic storage medium and device for identifying damage to backup power equipment

Abstract

The present invention relates to a method (100) for identifying a damage of one of at least two backup electrical energy devices for a vehicle occupant protection device, comprising the following steps: charging (101) the at least two backup electrical energy devices to a test voltage level (V_Test); determining (102) the ambient temperature of the at least two backup electrical energy devices; detecting (103) the (total) capacity of the at least two backup electrical energy devices; identifying (104) the damage of the backup electrical energy device based on a smoothed average value of the (total) capacity depending on the determined ambient temperature and the detected (total) capacity; updating (105) the smoothed average value based on the determined ambient temperature and the detected (total) capacity.

Description

Technical Field

[0001] The present invention provides a method, a computer program, an electronic storage medium and a device for identifying a damaged one of at least two backup electrical energy devices for a vehicle occupant protection device. Background Art

[0002] DE 37 44 524 A1 discloses a method for testing the availability of a backup electrical energy device for controlling a vehicle occupant protection device.

[0003] Herein, in order to check the capacity of the backup electrical energy device (capacitor), the backup electrical energy device is discharged from a first voltage value (U S1 ) at a constant discharge current (I K ) to a predetermined second voltage value (U S2 ). The discharge time (t E ) is measured. Given that the charging resistance (R E ) is known, the current capacity of the backup electrical energy device can be calculated based on the measured values.

[0004] The device for controlling a vehicle occupant protection system (airbag system) is designed such that all known standard collisions can always be operated by the backup electrical energy device even in the event of an interruption of the electrical energy supply by taking into account all tolerances, and the set occupant protection devices, such as restraint devices (airbags), can be activated, and necessary information related to the collision can be stored in a data memory (electronic data recorder; EDR).

[0005] The backup electrical energy devices used for this purpose usually consist of two or more electrolytic capacitors in medium and large systems. Due to manufacturing processes, these electrolytic capacitors have large capacitance tolerances. Herein, typical values at the time of delivery are between 0% and 30% of the nominal tolerance. In the temperature range from -40°C to +105°C, the temperature dependence is approximately 15%, for an equivalent load of 2000 h at 105°C, the capacity decreases by approximately 10% due to aging, and the DC factor (1.0 to 1.3) is the ratio of the DC capacity to the nominal capacity measured standardized at 120 Hz alternating current. Summary of the Invention

[0006] In this context, the present invention provides a method for identifying a damaged one of at least two parallel backup electrical energy devices for a device for controlling a vehicle occupant protection system.

[0007] In a system having only one electrolytic capacitor, the identification of a damaged electrolytic capacitor is known.

[0008] Known methods are not applicable to systems with two or more parallel electrolytic capacitors. This may be because the nominal capacitances of the individual capacitors may be different. However, even in a system with two or more parallel electrolytic capacitors having substantially the same nominal capacitance, the manufacturing-related capacitance tolerances are sufficient to render known methods for identifying damage unusable with the required reliability.

[0009] Accordingly, it is an object of the present invention to identify mechanical losses due to damage (e.g., due to vibrations, etc.) in a system having two or more parallel electrolytic capacitors as electrical energy storage, and to trigger a suitable warning device (e.g., an alarm light) or other service information to prompt error clearing or replacement of the control unit, even though the energy storage is not less than or has not fallen below a minimum value that meets all requirements.

[0010] Thereby, it is possible to prevent failures of the electronic system / sensor system due to movement of relatively heavy components (typical weight of electrolytic capacitors: about 10 g to 20 g) before such failures negatively affect the availability of the control device in the event of a collision.

[0011] This object is achieved by the method according to the invention.

[0012] For this purpose, the method comprises the following steps:

[0013] Charge at least two electrical energy storage devices to a test voltage level (V_Test);

[0014] Determine the ambient temperature of at least two electrical energy storage devices;

[0015] Detect the (total) capacitance of at least two electrical energy storage devices;

[0016] Identify damage to the electrical energy storage devices based on a smoothed average of the total capacitance that depends on the determined ambient temperature and the detected total capacitance;

[0017] Update the smoothed average based on the determined ambient temperature and the detected total capacitance.

[0018] The present invention is based on the recognition that the capacitance of electrical energy storage devices is temperature-dependent. Thus, by taking into account the ambient temperature of the electrical energy storage devices, it is possible to advantageously detect temperature-related changes in capacitance measurements from vehicle start-up to vehicle start-up and to reliably identify damage to at least one of the at least two electrolytic capacitors with the aid of the deviation between the temperature-related current capacitance value and the average capacitance value under substantially the same temperature conditions.

[0019] According to one embodiment of the method according to the invention, in the step of determining the ambient temperature, the temperature value of a temperature sensor of a sensor unit of the detection device is detected.

[0020] In this document, the sensor unit should be understood as a sensor that is not initially a temperature sensor. A device for controlling a vehicle occupant protection device (airbag control unit) typically has sensors for detecting forces acting on the vehicle (mainly acceleration sensors and yaw rate sensors). These sensors are sensor units in the sense of the present invention. These sensors can have circuits capable of sensing temperature values. This embodiment of the method of the present invention uses such a circuit of such a sensor to determine the ambient temperature. Here, this embodiment is based on the following recognition: on the one hand, the exact ambient temperature of the standby electrical energy device is not necessary for this method, and on the other hand, such sensors are arranged in a position adjacent to the standby electrical energy device or at least in the same housing as the control device, so that a sufficiently reliable temperature value can be provided for the ambient temperature of the standby electrical energy device.

[0021] According to an embodiment of the method of the present invention, in the step of determining the ambient temperature, a temperature value of a temperature sensor that detects the interior temperature of the vehicle is detected.

[0022] The advantage of this embodiment is that in many vehicles, especially in vehicles with air conditioning equipment, the temperature value of the interior temperature of the vehicle already exists, and this value can be accessed in a simple manner through an existing communication interface (such as via CAN, CAN-FD, FlexRay, Ethernet, etc.).

[0023] Although the temperature value of the interior temperature does not represent the exact value of the ambient temperature of the standby electrical energy device, this temperature value is sufficiently reliable for the implementation of the present invention.

[0024] According to an embodiment of the method of the present invention, in the step of determining the ambient temperature, a temperature grade is determined based on the detected temperature value.

[0025] This embodiment is based on the following recognition: in order to reliably identify the damage of at least one of at least two standby electrical energy devices for a vehicle occupant protection device control device, a temperature grade must be assigned to the ambient temperature of the standby electrical energy device, and a temperature-related capacity measurement and a temperature-related comparison are performed based on the assigned temperature grade.

[0026] This embodiment is based on the following recognition: the damage of the standby electrical energy device can be reliably identified with a relatively small number of temperature grades. For example, there are only three temperature grades for a low temperature range (-40°C to 0°C), normal (0°C to +40°C), and high (+40°C to +80°C).

[0027] Thus, this embodiment has the following advantages. On the one hand, only a few average values need to be maintained, that is, only one average value for each temperature level. On the other hand, the average values can be easily updated because the temperature values can be determined reliably enough for each temperature range, and then these temperature values can be considered to calculate the average value.

[0028] In one embodiment of the method according to the invention, in the updating step, the detected total capacity is considered for updating the smoothed average value only when the determined ambient temperature is lower than a predetermined threshold of the ambient temperature.

[0029] If the temperature value of the ambient temperature is higher than the predetermined threshold, the higher ambient temperature will affect the tolerance of the backup power equipment, making it impossible to perform meaningful capacity measurements in a cost-effective manner. Thus, it is also meaningless to consider the capacity values detected at such an ambient temperature for updating the temperature-related smoothed average value.

[0030] In one embodiment of the method according to the invention, in the updating step, the detected total capacity is considered for updating the smoothed average value only when the detected total capacity is within a predetermined tolerance range of at least two backup power equipment.

[0031] If the currently detected capacity is not within the predetermined tolerance range of the capacity, whether there is damage to the backup power equipment is irrelevant because in this case there is a serious failure of the entire backup power equipment. In this case, it is meaningless to consider the capacity values detected at such an ambient temperature for updating the temperature-related smoothed average value.

[0032] In one embodiment of the method according to the invention, in the updating step, the detected (total) capacity is considered for updating the smoothed average value only when the detected total capacity is within a predetermined tolerance range of the smoothed average value of the total capacity depending on the determined ambient temperature.

[0033] The temperature-related detection of the capacitance has a limited magnitude, so the individual capacity measurement values of the control unit will also be correspondingly scattered. If the scatter value is too high, it indicates a special situation that may cause measurement interference. Such measurement values can be identified by this embodiment and thus not considered for updating the temperature-related smoothed average value.

[0034] The above three embodiments are based on the recognition that the temperature-related smoothed average value of the capacity of the previous vehicle start is a central variable for identifying damage to the backup power equipment. To make the method more robust, the currently detected capacity value must meet any combination of the above conditions to be considered when calculating the smoothed average value. Through these embodiments, the temperature-related smoothed average value can be effectively prevented from being diluted by individual outliers when detecting the current capacity.

[0035] Another aspect of the present invention is a computer program which is arranged to perform all steps of the method according to the present invention.

[0036] Another aspect of the present invention is an electronic storage medium on which a computer program according to the present invention is stored.

[0037] Another aspect of the present invention is a control device which is arranged to perform all steps of the method according to the present invention. Description of the Drawings

[0038] The embodiments of the present invention will be described in more detail with reference to the accompanying drawings below.

[0039] Figure 1 A flowchart showing an embodiment of the method of the present invention is shown. Detailed Embodiments

[0040] Figure 1 A flowchart showing an embodiment of the method 100 of the present invention is shown.

[0041] The method starts in a state where the standby electrical energy device ER is charged to a predetermined target voltage level VER for operating a device (airbag control unit) for controlling a vehicle occupant protection device.

[0042] In step 101, at least two standby electrical energy devices ER are charged to a predetermined target voltage V_TEST for a capacity test. The standby electrical energy device ER can be an electrolytic capacitor. The target voltage V_TEST for the capacity test can be, for example, 11V. The charging can be controlled by a microcontroller μC of the airbag control unit. The μC can control the charging by transmitting corresponding control instructions to a charging circuit for charging the standby electrical energy device ER via SPI (Serial Peripheral Interface).

[0043] In step 102, the ambient temperature of at least two standby electrical energy devices ER is determined before the actual capacity measurement starts.

[0044] For this purpose, the μC can read the temperature of the system ASIC via SPI. Here, in addition to the μC, the system ASIC is also the central computing resource of the airbag control unit. The system ASIC of the airbag control unit generally includes a circuit for detecting the temperature value of the system ASIC. Since the system ASIC and the standby electrical energy device ER are usually arranged in close proximity to each other, at least within the same housing of the airbag control unit, this temperature value can be used to determine the ambient temperature of at least two energy storage devices. As an alternative to the system ASIC, a second μC or microprocessor μP with a redundant design, if necessary, can also be arranged in the airbag control unit.

[0045] The temperature value of the read system ASIC minus the self-heating of the ASIC reflects the ambient temperature of at least two backup power devices.

[0046] Alternatively or additionally, the μC can also access one or all of the temperature sensors of the sensor unit used within the housing of the airbag control unit. These reflect the internal temperature of the control unit with little or no correction, since there is almost no self-heating.

[0047] Alternatively or additionally, temperature values inside the vehicle can be accessed via a communication interface (such as CAN, CAN-FD, FlexRay, Ethernet, etc.).

[0048] According to the present invention, the ambient temperature determined before the start of the actual capacity measurement is used to determine temperature-dependent damage identification.

[0049] In step 103, the capacity of at least two backup power devices ER is detected. This detection is carried out by applying an appropriate charging current within an appropriate detection time. The parameters of the charging current and the detection time highly depend on the design of the backup power device ER and the charging circuit. Since these parameters are the same here as in the case of the known capacity measurement of a single electrolytic capacitor, the determination of the appropriate charging current and the appropriate detection time is within the scope of the art. These parameters are defined by the μC within the scope of measurement control and are transmitted to the charging or measurement circuit, for example, via SPI.

[0050] One possibility for detecting the capacity is to compare the voltage of the backup power device before the charging current for measurement is about to be applied with the voltage of the backup power device immediately after the end of an appropriate measurement time. The capacity of the backup power device can be directly determined from this voltage difference. For this purpose, the detected voltages can be stored in a suitable register of the μC for comparison after digitization.

[0051] In the step of detecting the capacity, it can be considered to check whether the detected capacity meets the predetermined minimum and maximum thresholds of the capacity.

[0052] The determined capacity value must be within the allowed range, which is determined by the minimum threshold Cg min and the maximum threshold Cg max of the total capacity.

[0053] Example: A backup power device with 6 parallel electrolytic capacitors has a nominal capacitance of 4.5 mF each at 120 Hz Cn. Thus, the total nominal capacitance Cgn is Cgn = 6 × 4.5 mF = 27 mF. The nominal tolerance is 0% to 30%; the Cgn temperature correlation is approximately + / -5%, the measurement current tolerance is + / -10%, the ER differential voltage measurement tolerance is + / -1%; the ADC accuracy is + / -1 bit ≈ + / -2.5%; the ER leakage current at the moment of measurement is between 0% and 10%, the tolerance of the DC capacitance value relative to the AC nominal value = 1.0 to 1.3; due to aging, an additional tolerance of 0% to 10% must also be considered.

[0054] Thus, the maximum threshold is Cg max = 1.3 × 1.05 × 1.10 × 1.01 × 1.025 × 1.1 × 1.30 × 27 mF = 60 mF;

[0055] The minimum threshold Cg min = 1 × 0.95 × 0.9 × 0.99 × 0.975 × 1 × 1 × 0.9 = 20 mF.

[0056] If the detected capacitance exceeds the predetermined range, there is a fault in the backup power device that requires appropriate fault handling, regardless of whether there is damage to the backup power device.

[0057] Here, such fault handling can include repeating the capacitance measurement. It is conceivable that a determined maximum number of repetitions of the capacitance measurement can be predetermined before the fault handling enters a higher escalation level. At a higher level, a warning can be issued, for example, by controlling a warning light, which will require a visit to a repair shop that provides appropriate equipment.

[0058] In step 104, damage to the backup power device is identified. According to the present invention, this identification is performed by comparing the currently temperature-dependent detected capacity of the backup power device with the temperature-dependent average capacity. If the currently detected capacity is lower than the temperature-dependent average capacity by more than a predetermined threshold AB_LIMIT, damage is identified. Because this deviation is not attributable to the temperature-related tolerance of the backup power device, but due to damage to at least one of the at least two backup power devices.

[0059] The following relationship applies to this identification:

[0060] Cg(θx,k) ∈ [Cg min (θx,k - 1), MWg_CG(θx,k - 1) - AB_LIMIT]; where:

[0061] Cg min : the minimum value of the total capacity of the backup power device

[0062] Cg(θx,k): The total capacity currently detected in the k-th measurement at temperature level θx (where x ∈ (n: low, c: normal, h: high));

[0063] MWg_CG(θx,k - 1): The smoothed average of the total capacity based on the (k - 1)-th measurement at temperature level x

[0064] AB_LIMIT: The threshold for capacity measurement, which indicates the damage of at least one of the backup power devices

[0065] The predetermined threshold AB_LIMIT for identifying the damage of at least one of the backup power devices can refer to the maximum capacity Cg max is predetermined in a simple and robust manner.

[0066] Due to the combined measurement uncertainty of approximately + / - 6.5%, it makes sense to adapt the threshold for identifying damage to this inaccuracy. For example, through the following simple and robust relationship:

[0067] AB_LIMIT = 0.065 × Cg max

[0068] For the example with one backup power device given above, where the total nominal capacity is Cgn = 6 × 4.5 mF = 27 mF nominal capacity and the maximum capacity is Cg max = 60 mF, there is:

[0069] AB_LIMIT = 0.065 × 60 mF = 3.9 mF.

[0070] Here, the temperature correlation can be considered by selecting the temperature level θx according to the detected temperature. For each temperature level θx, the capacity average of the previous capacity measurements can be available. The average can be a smoothed average.

[0071] Three temperature levels θx, for example, θn: low (-40 °C to 0 °C), θc: normal (0 °C to +40 °C), θh: high (+40 °C to +80 °C) have been proven sufficient to achieve reliable damage identification by means of the method of the present invention.

[0072] When considering the temperature level, a threshold for identifying damage can be set for each temperature level. To this end, the smoothed average can be obtained according to the following conditions:

[0073] AB_LIMIT(θx) = 0.065 × MWg_CG(θx,k - 1); where

[0074] MWg_CG(θx,k-1): The smoothed average of the total capacity based on the (k - l)-th measurement at temperature level θx

[0075] θx: Temperature level, where x ∈ (n: low, c: normal, h: high)

[0076] In addition, a threshold for the temperature can be considered as follows, i.e., above this threshold, reliable damage identification is no longer meaningful. This threshold can be, for example, the upper limit of the hottest temperature level (e.g., +80 °C). Above this threshold, the measurement error in determining the temperature is too large. In addition, at very high temperatures, the tolerances of electrolytic capacitors often become too complex to enable meaningful damage detection. If the threshold is set high enough, the actual occurrence of such high-temperature situations is impossible.

[0077] If no damage to the backup power supply device is identified in step 104, the smoothed average is updated in step 105. Here, this update is temperature-dependent. In the case of achieving temperature dependence by means of temperature levels, the temperature-dependent update is performed by updating the smoothed average of the assigned temperature level with the currently determined capacity value. Thus, the smoothed averages of the remaining temperature levels are not updated with the currently determined capacity value.

[0078] To make the smoothed average of the total capacity more robust, the currently detected total capacity can be considered for updating the smoothed average only when the determined ambient temperature is below a predetermined threshold of the ambient temperature.

[0079] For this purpose, it is recommended to use a value of 80 °C as the threshold. Above this value, the tolerance characteristics of the electrolytic capacitor are so complex that damage cannot be identified with reasonable resource utilization. In addition, such a high ambient temperature is very rare, especially when the vehicle starts.

[0080] To make the smoothed average of the total capacity more robust, the currently detected total capacity can be considered for updating the smoothed average only when the currently detected total capacity is within the predetermined tolerance range of at least two backup power supply devices.

[0081] It is recommended to use the range of the absolute minimum capacity (Cg min ) and the maximum capacity (Cg max ) of the airbag control unit as the tolerance range. Here, the typical values are Cg min = 20 mF and Cg max = 60 mF.

[0082] To make the smoothed average of the total capacity more robust, the currently detected total capacity can be considered for updating the smoothed average only when the currently detected total capacity is within the predetermined tolerance range of the smoothed average of the total capacity depending on the determined ambient temperature.

[0083] The temperature-related detection of the capacity has a limited size, so the individual capacity measurement values of the control unit will also be correspondingly scattered. If the scattered value is too high, it indicates a special situation that may cause measurement interference. Such measurement values can be identified by this embodiment and thus are not considered for updating the temperature-related smoothed average value.

[0084] For example, the following can be applied to the tolerance range:

[0085] Cg(θx,k) ∈ [MWg_Cg(θx,k - 1) - 0.4 * AB_LIMIT, MWg_Cg(θx,k - 1) + 0.4 * AB_LIMIT]; where:

[0086] Cg(θx,k): the total capacity currently detected in the k-th measurement at the temperature level θx (where x ∈ (n: low, c: normal, h: high));

[0087] MWg_CG(θx,k - 1): the smoothed average value of the total capacity based on the (k - l)-th measurement at the temperature level x;

[0088] AB_LIMIT: the threshold value of the capacity measurement, which indicates the damage of at least one of the backup power devices among at least two backup power devices.

Claims

1. A method (100) for identifying a damaged one of at least two backup electrical energy devices for a vehicle occupant protection device, wherein the at least two backup electrical energy devices are connected in parallel and the at least two backup electrical energy devices have a capacitance tolerance related to manufacturing, comprising the steps of: charging (101) the at least two backup electrical energy devices to a test voltage level (V_Test); determining (102) the ambient temperature of the at least two backup electrical energy devices; detecting (103) the total capacitance of the at least two backup electrical energy devices; identifying (104) a damaged backup electrical energy device by comparing a smoothed average value of the total capacitance, which depends on the determined ambient temperature, with the detected total capacitance; updating (105) the smoothed average value according to the determined ambient temperature and the detected total capacitance, wherein the detected total capacitance is considered for updating the smoothed average value only if the detected total capacitance is within a predetermined tolerance range of the at least two backup electrical energy devices, or only if the detected total capacitance is within a predetermined tolerance range of the smoothed average value of the total capacitance that depends on the determined ambient temperature.

2. The method according to claim 1, wherein a damaged backup electrical energy device is identified when the degree to which the detected total capacitance is lower than the temperature-related smoothed average value exceeds a predetermined threshold for identifying damage.

3. The method according to claim 1 or 2, wherein in the step of determining the ambient temperature, a temperature value of a temperature sensor of a sensor unit of the device is detected, wherein the sensor unit is arranged to detect a force acting on the vehicle and the sensor unit has a circuit capable of detecting a temperature value as the temperature sensor.

4. The method according to claim 1 or 2, wherein in the step of determining the ambient temperature, a temperature value of a temperature sensor is detected, the temperature sensor detecting the interior temperature of the vehicle.

5. The method according to claim 1 or 2, wherein in the step of determining the ambient temperature, a temperature class for a temperature range is determined according to the detected temperature value, wherein based on the assigned temperature class, the detection of the total capacitance of the at least two backup electrical energy devices and the temperature-related comparison are performed to identify a damaged backup electrical energy device.

6. The method according to claim 5, wherein three temperature classes are used for the temperature range: -40°C to 0°C; 0°C to +40°C; +40°C to +80°C.

7. The method according to claim 6, wherein each temperature class is assigned a smoothed average value of the total capacitance and a threshold for identifying damage is set for each temperature class, wherein a damaged backup electrical energy device is identified when the degree to which the detected total capacitance for the temperature class is lower than the temperature-related smoothed average value for the temperature class exceeds a predetermined threshold for identifying damage.

8. The method according to claim 1 or 2, wherein in the updating step, the detected total capacity is considered to update the smoothed average only when the determined ambient temperature is lower than a predetermined threshold of the ambient temperature.

9. The method according to claim 1 or 2, wherein each time the vehicle is started, the method for identifying a failure of one of at least two backup electrical energy devices is repeated, and the smoothed average related to temperature is from a previous vehicle start.

10. A computer program product, configured to perform all steps of the method (100) according to any one of claims 1 to 9.

11. An electronic storage medium, on which a computer program is stored, the computer program being configured to perform all steps of the method (100) according to any one of claims 1 to 9.

12. A device for identifying a failure of one of at least two backup electrical energy devices for vehicle occupant protection, configured to perform all steps of the method (100) according to any one of claims 1 to 9.

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